A vacuum pump such as a turbomolecular pump or a molecular drag pump discharges gas in a vacuum chamber by rotating a rotor with a discharge inducing system (a turbine vane unit and a molecular drag pump unit) constituted with turbine vanes and the like formed thereat, at high speed in the order of several tens of thousands of rpm.
If the rotor engaged in such high speed rotation breaks, the pump casing of the vacuum pump will be subjected to extreme high energy. The impact of such energy may be transmitted, via the pump casing, to a vacuum device to which the vacuum pump is connected and may cause damage on the vacuum device side. This concern is addressed in a structure known in the related art that includes a fragile part constituted with a groove, located at a screw groove spacer fixed to a base and assuming a position facing opposite the rotor outer circumference, so as to reduce the shock communicated to the device side by causing a shear fracture at the fragile part (see, for instance, patent literature 1).
Patent literature 1: Japanese Laid Open Patent Publication No. 2006-170217